1. Field of the Invention
The present invention relates to a resin hose connection method and a resin hose connection structure produced by employing the method.
2. Description of the Art
Conventionally, a hose to be connected to a metal pipe such as of a pressure regulator or a fuel strainer of an automobile is composed of a highly elastic rubber. Recently, an attempt has been made to suppress gasoline permeation and to achieve weight reduction and cost reduction by employing a resin hose instead of the conventional rubber hose.
However, the resin hose has a lower elasticity than the rubber hose, so that insertion of the metal pipe into the hose is less easy and the sealing property of the hose with respect to the metal pipe is inferior.
In view of the foregoing, it is an object of the present invention to provide a resin hose connection method and a resin hose connection structure produced by the method, which ensure easy insertion of the metal pipe into the hose and an excellent sealing property.
In accordance with a first aspect of the present invention to achieve the aforesaid object, there is provided a method of connecting a resin hose to a metal pipe, the method comprising the steps of: forming a fluororubber coating layer on an inner peripheral surface of the resin hose; forming a lubricating layer of a fluorine-containing lubricant on an inner peripheral surface of the fluororubber coating layer; and inserting an end portion of the metal pipe into an end portion of the resin hose formed with the lubricating layer.
In accordance with a second aspect of the present invention, there is provided a resin hose connection structure comprising: a resin hose; a fluororubber coating layer provided on an inner peripheral surface of the resin hose; a metal pipe inserted in the resin hose; and a trace of a fluorine-containing lubricant present in an interface between the fluororubber coating layer and the metal pipe, the fluorine-containing lubricant having been present as a lubricating layer between the fluororubber coating layer and the metal pipe at insertion of the metal pipe into the resin hose and finally diffused in the fluororubber coating layer.
The inventors of the present invention have conducted intensive studies on a resin hose connection method which ensures easy insertion and an excellent sealing property. In the course of the studies, the inventors found that, where a fluororubber coating layer is formed on an inner peripheral surface of the resin hose, fluorine atoms in a fluororubber molecular skeleton are hydrogen-bonded to hydroxyl groups of a metal of a metal pipe to enhance adhesion between the resin hose and the metal pipe for improvement of the sealing property. However, insertion of the metal pipe into the hose cannot be facilitated simply by forming the fluororubber coating layer on the inner peripheral surface of the resin hose. The inventors have come up with an idea of additionally forming a lubricating layer on an inner peripheral surface of the fluororubber coating layer for easier insertion of the metal pipe. Where dimethyl silicone or the like is employed as the lubricant, however, the fluororubber coating layer is separated from the hose when the lubricant is applied on the fluororubber coating layer. Therefore, the adhesion between the fluororubber coating layer and the resin hose is deteriorated, so that the easy insertion and the sealing property cannot simultaneously be ensured. Further research and development conducted by the inventors have revealed that, where a fluorine-containing lubricant is employed as the lubricant, the fluororubber coating layer is not separated when the lubricant is applied on the inner peripheral surface of the fluororubber coating layer, so that the easy insertion and the sealing property can simultaneously be ensured without the deterioration of the adhesion between the fluororubber coating layer and the resin hose. Further, it has been found that the lubricating layer of the fluorine-containing lubricant facilitates the insertion of the metal pipe when the hose is connected to the metal pipe and, after the connection, the fluorine-containing lubricant penetrates into the fluororubber coating layer formed on the inner peripheral surface of the resin hose so that the lubricating layer disappears. Therefore, hydrogen bonds are sufficiently formed in the interface between the metal pipe and the fluororubber coating layer on the inner peripheral surface of the resin hose. Thus, the present invention has been attained.